Large-area individually addressable multi-beam x-ray system and method of forming same

ABSTRACT

A structure to generate x-rays has a plurality of stationary and individually electrically addressable field emissive electron sources with a substrate composed of a field emissive material, such as carbon nanotubes. Electrically switching the field emissive electron sources at a predetermined frequency field emits electrons in a programmable sequence toward an incidence point on a target. The generated x-rays correspond in frequency and in position to that of the field emissive electron source. The large-area target and array or matrix of emitters can image objects from different positions and/or angles without moving the object or the structure and can produce a three dimensional image. The x-ray system is suitable for a variety of applications including industrial inspection/quality control, analytical instrumentation, security systems such as airport security inspection systems, and medical imaging, such as computed tomography.

RELATED APPLICATION DATA

This application is a continuation of U.S. patent application Ser. No.10/051,183, filed on Jan. 22, 2002, which is a continuation-in-part ofU.S. patent application Ser. No. 09/679,303, filed on Oct. 6, 2000, nowU.S. Pat. No. 6,553,096. The entire disclosures of both referencedapplications are incorporated herein by reference.

STATEMENT REGARDING GOVERNMENT SUPPORT

At least some aspects of this invention were made with Governmentsupport under contract no. N00014-98-1-05907. The Government may havecertain rights in this invention.

FIELD OF THE INVENTION

The present invention relates to a method and device for generating andcontrolling x-ray radiation. For example, the present invention relatesto a method and device that generates electron emission from an array ormatrix of emitters. Emitted electrons directly impact differentlocations on a large-area target to produce multiple x-ray beams fromdifferent origins and thereby providing improved imaging capabilities,including dynamic imaging.

BACKGROUND OF THE INVENTION

In the description of the background of the present invention thatfollows reference is made to certain structures and methods, however,such references should not necessarily be construed as an admission thatthese structures and methods qualify as prior art under the applicablestatutory provisions. Applicants reserve the right to demonstrate thatany of the referenced subject matter does not constitute prior art withregard to the present invention.

The term “nano-structured” or “nanostructure” material is used by thosefamiliar with the art to designate materials including nanoparticleswith a particle size or less than 100 nm, such as nanotubes (e.g.—carbonnanotubes). These types of materials have been shown to exhibit certainproperties that have raised interest in a variety of applications.

Current x-ray tubes comprise a target with a single (or dual) focalpoint(s) (where electrons bombard a target and x-rays are emitted), andeither a single cathode or dual cathodes. Electrons are generallythermionically emitted from the cathode(s) and are focused to impact asmall area on the target. For imaging or diagnostic purposes over alarge area, either the object or the x-ray tube (or both) has to bemoved over the area.

One example of such a use for x-rays includes computed tomography (CT).FIGS. 1 (a-d) depict the general arrangement of a CT scanner 100 inwhich an x-ray source 102 (typically an x-ray tube) is rotated(direction indicated by the arrow) about the object to be imaged 104.The data can be collected by either a single detector 106 coordinatelymoving with the x-ray source 102 (see FIG. 1 a), multiple detectors 106coordinately moving with the x-ray source 102 (see FIGS. 1 b and 1 c),or multiple stationary detectors 106 (see FIG. 1 d). As a consequence ofthe current CT designs, the scanners are usually large with complicatedmechanical systems. Scanners can be limited by the rotation speed of thex-ray tube and by the size and weight of the apparatus. This lastlimitation can adversely affect the capture of clear images of movingparts, such as a beating heart.

Dynamic three-dimensions (3D) images can be acquired by so-called “fifthgeneration CT scanners.” An example of a 5^(th) generation CT scanner200 is shown in FIG. 2. An electron beam 202 is produced by a stationaryelectron gun 204 in a vacuum system 206. The electron beam 202 isfocused by a focus coil 208 and scanned by a deflection coil 210 suchthat the applied magnetic field positions the electron beam 202 acrossany one of several stationary metal target rings 212 from which an x-rayis emitted. The emitted x-rays 214 project toward the object 216 to beimaged and are detected by a stationary detector 218 and processed by adata acquisition system 220. Although such a system is capable ofproducing dynamic 3D images, the scanner 200 is very large and costly tofabricate.

In addition to the design limitations of current CT scanners, currentx-ray sources use heated metal filaments as the sources of electrons.Because of the thermionic emission mechanism, a very high operatingtemperature is required, typically in the order of 1000-1500° C. Thehigh operating temperatures results in problems such as short lifetimeof the filament, slow response time (i.e., time to warm up the filamentbefore emission), high-energy consumption, and large device size.

Further, because of the fundamental physics of the thermionic emissionmechanism, electrons are emitted in all directions. In x-ray tubeapplications, an additional electrical field can be applied to bring theelectrons into focus at the target, but with attendant complexity andcost. Additionally, such conventional techniques of focusing electronbeams have certain disadvantages, such as limits on the uniformity andsize of the focusing spots.

Carbon nanotube materials have been shown to be excellent electron fieldemission materials. In this regard, carbon nanotube materials have beenshown to possess low electron emission threshold applied field values,as well as high emitted electron current density capabilities,especially when compared with other conventional electron emissionmaterials.

Commonly owned U.S. Pat. No. ______ (Ser. No. 09/296,572 entitled“Device Comprising Carbon Nanotube Field Emitter Structure and Processfor Forming Device”) the disclosure of which is incorporated herein byreference, in its entirety, discloses a carbon nanotube-based electronemitter structure.

Commonly owned U.S. Pat. No. ______ (Ser. No. 09/351,537 entitled“Device Comprising Thin Film Carbon Nanotube Electron Field EmitterStructure”), the disclosure of which is incorporated herein byreference, in its entirety, discloses a carbon-nanotube field emitterstructure having a high emitted current density.

Commonly owned U.S. Pat. No. 6,277,318 entitled “Method for Fabricationof Patterned Carbon Nanotube Films,” the disclosure of which isincorporated herein by reference, in its entirety, discloses a method offabricating adherent, patterned carbon nanotube films onto a substrate.

Commonly owned U.S. Pat. No. ______ (Ser. No. 09/679,303 entitled “X-RayGenerating Mechanism Using Electron Field Emission Cathode”), thedisclosure of which is incorporated herein by reference, in itsentirety, discloses an X-ray generating device incorporating ananostructure-containing material.

Thus, there is a need in the art to address the above-mentioneddisadvantages associated with methods and devices for generating x-raysand for applying x-rays in applications in imaging environments, such ascomputed tomography. Further, there is a need in the art for imagingsolutions in both static and dynamic environments.

SUMMARY OF THE INVENTION

A structure to generate x-rays with a target and an opposing surface hasa plurality of stationary and individually electrically addressableelectron sources defining a plurality of cathodes. The structure togenerate x-rays can be an x-ray source in a device to record x-rayimages. The electron source is preferably a field emission electronsource and can be a triode-type having a substrate composed of a fieldemissive material and a gate electrode positioned parallel to andinsulated from the substrate. The field emissive material is preferablya material that has a low threshold field for emission and is stable athigh emission currents. For example, the field emissive material can becarbon nanotubes such as single wall, double wall, or multi-wall carbonnanotube, nanowires or nanorods of metal, metal oxide, silicon, siliconoxide, carbide, boride, nitride, or chalcogenide. Additionally,nanostructure containing materials formed from silicon, germanium,aluminum, silicon oxide, germanium oxide, silicon carbide, boron, boronnitride, and boron carbide can be the field emissive material. Thecathodes and the target are housed in an evacuated chamber with multiplewindows that are transparent to x-rays.

The electrons emitted from the stationary cathodes are accelerated toand impact on different points of the target by the voltage appliedbetween the target and the cathodes. The target area or a particulartarget from amongst multiple targets where an electron impacts can becontrolled or selected by a suitable design of cathodes and targetgeometry, or by applying additional focusing electric fields, or othersuitable techniques. Upon impact by the electrons, x-ray radiation isemitted from the impact surface of the target materials. Direction anddivergence of the x-ray radiation can be controlled by the location ofthe windows and collimators with respect to the chamber.

The intensity of the x-ray radiation depends on the voltage appliedbetween the target and the cathode, and the emitted electron current.The emitted electron current from the emissive materials is controlledby the electrical field between the gate electrode and the fieldemissive material in the triode configuration or between the target andthe field emissive material in the diode case. The field emittedelectrons are essentially non-divergent and travel toward the gateelectrode and anode. The emission can occur at 300K and can be rapidlyswitched on and off by controlling the electric field applied.

In one embodiment, a method of generating an x-ray image positions anobject within an imaging zone, switches each of a plurality of cathodeson a stationary cathode structure at a predetermined frequency to fieldemit an electron, emits an x-ray from a target of the stationary targetstructure at the predetermined frequency, images the object, and detectsthe emitted x-ray. Each of the plurality of cathodes comprises a fieldemissive electron source is individually addressable and electricallyswitched in a programmable sequence to field emit electrons toward anincidence point on a stationary target structure.

In another embodiment, a method for obtaining an x-ray image places anobject in an x-ray source, applies power to at least one of theplurality of cathodes to generate x-ray radiation for a pre-set orvariably-set exposure time, exposes the object to the x-ray radiation,and captures an x-ray image corresponding to the object by either anx-ray detector or an x-ray sensitive film.

In one aspect, the x-ray detector or x-ray sensitive film moves at acorresponding frequency to the pre-set or variably-set frequency appliedto the cathode to capture an image and/or detect an x-ray.Alternatively, the x-ray detector or x-ray sensitive film is stationaryand the individual, group, or portions of the individual or group ofx-ray detectors or x-ray sensitive films are activated (e.g., enabled todetect and/or capture) at a corresponding frequency to the pre-set orvariably-set frequency applied to the cathode to capture an image and/ordetect an x-ray.

In a further aspect, the position on the stationary target structurefrom which the x-ray emits corresponds spatially and temporally to aposition on the cathode structure from which the electron emits and atleast one of a circumferential position and an elevation angle of theemitted x-ray is sufficiently discriminated with respect to the objectto produce a three dimensional image.

In an additional aspect, power is applied to all of the plurality ofcathodes simultaneously or to a subset of the plurality of cathodessequentially at a pre-set or variably-set frequency. In the latter, thex-ray detector or the x-ray sensitive film is moved or activated at acorresponding frequency to the pre-set or variably-set frequency tocapture the x-ray image. The frequency can be sufficiently rapid todynamically image a physiological function.

The x-ray system can have a large-area target and an array or matrix ofemitters. Electrons are emitted directly towards different incidencepoints on the target to produce multiple x-ray beams from differentorigins. The result is that images of a large object can be taken fromdifferent areas and/or angles without moving the object or the x-raytube. The x-ray system is suitable for a variety of applicationsincluding industrial inspection/quality control, analyticalinstrumentation, security systems such as airport security inspectionsystems, and medical imaging, such as computed tomography.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

Other objects and advantages of the invention will become apparent fromthe following detailed description of preferred embodiments inconnection with the accompanying drawings in which like numeralsdesignate like elements and in which:

FIGS. 1(a)-(d) represent computed tomography systems in which the x-raysource and/or the detector are rotated about an object to be imaged.

FIG. 2 is a representative example of a fifth generation computedtomography system.

FIG. 3 is an embodiment of a structure to generate x-rays.

FIG. 4 a cross sectional view of an embodiment of a device to recordx-ray images.

FIG. 5 is an embodiment of a cathode structure.

FIG. 6 is a schematic of the details of the target structure.

FIG. 7 is a first schematic representation of generated x-rays imagingan object.

FIG. 8 is second schematic representation of generated x-rays imaging anobject

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A structure to generate x-rays comprises a plurality of stationary andindividually electrically addressable electron sources defining aplurality of cathodes, at least one target placed opposing the cathodes,and an evacuated chamber that houses the plurality of cathodes and theat least one target. The electron sources can be filed emission electronsources and can be triode-type or diode-type structures.

FIG. 3 is an embodiment of a structure 300 to generate x-rays. A cathodestructure 302 and a target structure 304 are disposed within a chamber306, which is substantially in the form of a hollow cylinder having anouter wall 308 and an inner wall 310. The cathode structure 302 and theanode structure 304 are positioned within the chamber 306 between theinner wall 308 and the outer wall 310. The chamber 306 is operationallymaintained at a vacuum of at least 1 Torr by a suitable vacuum systemoperatively connected to the chamber 306. Feedthroughs (not shown), asknown in the art, can provide services to components within the chamber306.

A device to record x-ray images comprises an x-ray source having acathode structure and a target structure, an object positioning systemand a detector system. In one aspect the x-ray source can be a structureto generate x-rays as shown and described herein.

On example of an embodiment of a device to record x-ray images is shownin FIG. 4 in cross sectional view. The device 400 to record x-ray imageshas a cathode structure 402, a target structure 404, an objectpositioner 406, and a detector 408. The cathode structure 402 can be inthe form of a single cathode or a plurality of cathodes. In theembodiment shown, the cathode structure 402 is arranged as a ring tocorrespond to the overall shape of the chamber 410. Similar to thecathode structure 402, the target structure 404 can be in the form of asingle target or a plurality of targets. In the embodiment shown, thetarget structure 404 is arranged as a ring to correspond to the overallshape of the chamber 410. The target structure 404 can produce an x-ray412 of a desired wavelength upon bombardment by electrons 414 emittedfrom the cathode structure 402. The x-ray 412 propagates to an imagingzone 416 containing the object 418 to be imaged and is detected by thedetector 408. The detector 408 can be an array or matrix of x-raydetectors or x-ray sensitive films opposing the x-ray source, the arrayor matrix substantially parallel to and at equal distance to the x-raysource (e.g. the position from which x-rays propagate to the object). Inone aspect, the detector 408 can be located on the circumference of theimaging zone 416 adjacent to the inner wall 418 and outside of thechamber 410. In another aspect, the x-ray sources and detectors, can beon opposing parallel planes. The device 400 to record x-ray images issuitable for a variety of applications including industrialinspection/quality control, analytical instrumentation, security systemssuch as airport security inspection systems, and medical imaging, suchas computed tomography.

The cathode structure 402 can be any suitable geometric form having asurface 420 facing the target structure 404. For example, the cathodestructure 402 can be substantially an annulus, a torus, or a plate. Oneor more, field emissive electron sources can be affixed to the cathodestructure 402.

Where the cathode structure is a plane or is planar-like, the pluralityof cathodes and the at least one target can be each on an opposing planeand he target has a deflection surface that can be oriented toward asurface of the plurality of cathodes that emits electrons. In one aspectthe deflection surface is oriented nonparallel to the surface of theplurality of cathodes. Further, each of the plurality of cathodes can beindividually positioned on one of the opposing planes at apre-determined spatial interval.

Where the cathode structure is a ring or is ring-like, the plurality ofcathodes can be disposed on a first ring and the at least one target canbe disposed on a second ring, the first and second rings concentric, andthe at least one target has a deflection surface that can be orientedtoward a surface of the plurality of cathodes that emits electrons. Inone aspect, the deflection surface can be oriented non-parallel to thesurface of the plurality of cathodes. Further, each of the plurality ofcathodes can be individually positioned on one of the first or secondrings at a pre-determined spatial interval.

FIG. 5 shows an exemplary embodiment of a cathode structure 500 assubstantially an annulus 502 with multiple discreet field emissiveelectron sources 504 disposed on a broad facing surface 506. Each fieldemissive electron source 504 defines a cathode in an x-ray generatingapparatus. The field emissive electron sources 504 are each individuallyelectrically addressable and stationarily affixed to the cathodestructure 500. In the FIG. 5 embodiment, the field emissive electronsources 502 are arranged at intervals along the cathode structure 500.The interval (α) can be any suitable interval to obtain the desiredimaging results. Both fixed intervals and random intervals areenvisioned. In at least one exemplary embodiment, the interval betweensuccessive field emissive electron sources 504 is approximately 10°.

In the FIG. 5 embodiment, a recess 508 in the cathode structure 500 canhouse a planar circular field emissive material 510. Disposed parallelto the planar surface 512 of the field emissive material 510 andinsulated from it is a gate electrode 514. Further, the gate electrode514 can be disposed across a surface of the field emissive material 510substantially equidistant from the field emissive material 510. Thearrangement of field emissive material and gate electrode can be, forexample, a triode-type or diode-type structure. When above a thresholdvalue, a bias (e.g., electric field) between the field emissive material510 and the gate electrode 514 extracts and accelerates electrons fromthe cathode substantially perpendicularly to the planar surface 512 ofthe field emissive material 510. Accordingly, the field emittedelectrons are non-divergent. The plurality of field emitted electronspass the gate electrode and are further directed to a predeterminedposition and accelerated to impact on the at least one target by theelectric field applied between the gate electrode and the at least onetarget. Upon impact at an incidence point, at least one x-ray having acharacteristic wavelength corresponding to a material of the at leastone target and at least one x-ray having a continuous wavelength aregenerated.

The field emissive material 510 can be formed from any one of numerousnanostructure materials that possess high emission current densities.For example, the field emissive material can be carbon nanotubes (e.g.,single walled carbon nanotubes, double walled carbon nanotubes, ormulti-wall carbon nanotubes). Alternatively, the field emissive materialcan be a nanotube comprising at least one non-carbon element. Further,the field emissive material can be a nanorod/nanowire comprising atleast one of a metal, a metal oxide, silicon, silicon carbide, siliconoxide, carbon nitride, boron nitride, boron carbide, or a chalcogenideor can be other nanowires such as SiC or SiC nanowires. Additionally,nanostructures containing materials formed from silicon, germanium,aluminum, silicon oxide, germanium oxide, silicon carbide, boron, boronnitride, and boron carbide are contemplated. More specific details ofthe above-mentioned materials are disclosed in commonly owned U.S. Pat.No. ______; (Ser. No. 09/594,844; Attorney Docket No. 032566-003), thedisclosure of which is incorporated herein by reference in its entirety.

The field emissive material can be applied by any suitable technique andin any suitable geometric form. Examples of suitable techniques andforms are given in commonly owned U.S. Pat. No. 6,277,318, entitled“Method for Fabrication of Patterned Carbon Nanotube Films,” thedisclosure of which is incorporated herein by reference, in itsentirety, in which a method of fabricating adherent, patterned carbonnanotube films onto a substrate is disclosed. Further, it is known toform field emitting cathodes with various geometrical configurations,such as one or more sharp points or ridges which act to focus the beamof emitted electrons. See, for example, U.S. Pat. Nos. 3,921,022;4,253,221; and 5,773,921, the disclosures of which are incorporatedherein by reference. Additional suitable techniques include coating thefield emissive material on the substrate as a film, embedding the fieldemissive material in a matrix of the substrate, or forming the fieldemissive material as a free-standing substrate structure.

In an additional embodiment, the cathode structure can be a suitablestructural substrate material coated with a field emissive material andformed into the field emissive electron source. In this embodiment, thecathode structure can be formed as a continuous array or a matrix offield emissive materials and can be individually electricallyaddressable. For example, the structural material can have aninterdigitated array (IDA) of conductors with discrete surface areasexposed on the surface of the upper ring. Interdigitated arrays can befabricated for specific applications by photolithographic techniques andusing a lift-off process. Additionally, IDAs are commercially availablein standard forms from, for example, ABTECH Scientific, Inc., RichmondVa. A layer of field emissive material, such as single wall, double wallnanotubes, or multi-wall nanotubes, can be disposed on the structuralmaterial and can cover the discrete areas corresponding to exposedelectrical leads of the IDA. By electrically addressing the discreteareas individually or in programmed sequence, the field emissivematerial can be pulsed advantageously to produce field emissionelectrons that can be directed to particular areas on the target. Aninsulating layer and a gate electrode can be coated on the fieldemissive material by a physical vapor deposition technique or othersuitable technique. Alternatively, the gate electrode can be a separatestructure, such as a screen, that can be positioned adjacent theinsulating layer either abutting the insulting layer or with aseparation distance.

The field emissive electron source or cathode may be formed in anysuitable manner. For example, a carbon nanotube film can be formed bydepositing carbon nanotubes onto a substrate. The carbon nanotubes canbe deposited onto the substrate by any suitable means. An example of adeposition technique includes the use of an adhesion promoting layer. Anexample of an adhesion promoting layer is disclosed in commonly ownedU.S. Pat. No. ______ (Ser. No. 09/817,164), the disclosure of which isincorporated herein by reference in its entirety.

Numerous single wall nanotube fabrication techniques are envisioned. Forexample, the single wall nanotubes can be fabricated using a laserablation process. This technique is generally described, for example, inA. Thess et al., Science; 273, 483-487 (1996); C. Bower et al., AppliedPhysics, Vol. A67, 47 (1998); X. P. Tang et al. Science, Vol. 288, 492(2000), the disclosures of which are hereby incorporated by reference.Single wall carbon nanotubes can also be fabricated by arc-discharge(See, for example, C. Journet et al., Nature, Vol. 388, 756 (1997)) andchemical vapor deposition techniques (See, for example, A. M. Cassell etal. J. of Physical Chemistry B, 103, 6484 (1999)).

One particularly suitable technique of forming single wall nanotubesaccording to the present invention includes a technique as described incommonly owned U.S. Pat. No. ______ (Ser. No. 09/259,307; AttorneyDocket No. 032566-001) the disclosure of which is incorporated herein byreference, in its entirety.

According to this technique, a target made from graphite and a suitablecatalyst, such as nickel and/or cobalt is placed within a quartz tube.The target is formed from a graphite powder mixed with 0.6 atomicpercent nickel and 0.6 atomic percent cobalt, and graphite cement. Thetarget is then heated within the tube to a temperature of approximately1150° C. The tube is evacuated by means of a vacuum pump and a flow ofinert gas, such as argon, is introduced into the tube by a suitablesource. Various control devices may be attached to the system forcontrolling and monitoring the flow of inert gas into the tube, as wellas the vacuum within the tube. The pressure of the inert gas as ismaintained at a suitable level, such as approximately 800 torr.

An energy source, such as a pulsed Nd:YAG laser, is used to ablate thetarget at the above-described temperature. Preferably, the first and/orsecond harmonic beam of the laser, i.e. 1064 nm and 532 nm,respectively, are used to ablate the target.

As the target is ablated, nanotube-containing material is transporteddownstream by the inert gas flow, and forms deposits on the inner wallof the tube. These deposits are then removed to recover thenanotube-containing material. This material, as recovered, has beenanalyzed and found to contain 50-70 volume % of SWNTs with individualtube diameters of 1.3-1.6 nm and bundle diameters of 10-40 nm. Thebundles are randomly oriented.

The as-recovered materials are then purified by a suitable purificationprocess. In a preferred embodiment, the nanotube material is placed in asuitable liquid medium, such as an organic solvent, preferably analcohol such as methanol. The nanotubes are kept in suspension withinthe liquid medium for several hours using a high powered ultrasonichorn, while the suspension is passed through a micro porous membrane. Inanother embodiment, the carbon nanotube containing material is firstpurified by reflux in a suitable solvent, preferably 20% H₂O₂ withsubsequent rinsing in CS₂ and then in methanol, followed by filtration,as described in Tang et al., Science, Vol. 288, 492 (2000).

In addition to the above described processing steps, the purifiedmaterials can be further processed by milling, such as ball-milling oroxidation. The optional step of milling will of course act to createeven more broken nanotubes and theoretically at least even furtherincrease the number of ends of the nanotubes which are capable offorming sites for the emission of electrons toward an anode target. Thecarbon nanotubes can also be shortened by oxidation in strong acid. Thelength of the nanotubes can be controlled by the acid concentration andreaction time. In a preferred embodiment, the purified single wallcarbon nanotubes are sonicated in a solution of 3:1 volume ratio ofH₂SO₄ and HNO₃. The average nanotube length is reduced to 0.5 micron(from 10-30 micron in the as purified case) after 24 hours ofsonication. More emission tips per unit area can be obtained using theshort nanotubes.

Processing methods and considerations in forming an x-ray generatingmechanism using field emission cathodes are contained in commonly ownedU.S. Pat. No. ______ (U.S. patent application Ser. No. 09/679,303,Attorney Docket No. 032566-005), the disclosure of which is hereinincorporated by reference.

The target structure can have one or more targets, each corresponding toa field emissive electron source. FIG. 6 shows an exemplary targetstructure 600 in the form of the target structure cross section of FIG.4. In the exemplary embodiment shown, the target structure 600 issubstantially triangular in form with a deflection surface 602 thatgenerates x-rays from an incidence point 604. The deflection surface 602is oriented substantially non-perpendicularly to the propagationdirection of the accelerated electron beam incident to the deflectionsurface 602. Accordingly, a non-divergent and accelerated emittedelectron from the field emissive electron sources impacts the deflectionsurface 602 at an incidence point 604 at an angle β such that theemitted x-ray is propagated toward the imaging zone at a correspondingangle γ to the deflection surface 602.

The cathode structure and the target structure can be mounted within thechamber by suitable means. In one embodiment, the cathode structure andtarget structure are mounted directly to the interior surface of thechamber and are provided with suitable electrical insulation. In anotherembodiment, ceramic screws connect the upper ring to the lower ring. Anadditional ceramic screw can be used to affix the lower ring to aninterior surface of the chamber. One particularly suitable ceramic screwis approximately 5 cm in length and has insulating properties.

The detector can be any suitable x-ray detecting means. For example, thedetector can be a rotatable detector that can be positionedcircumferentially to the object to be imaged and opposite to theincidence point of the electron beam on the target structure. In anotherexample, the detector can be an array or matrix of x-ray detectors orx-ray sensitive films stationarily positioned opposite the x-ray sourceand in line with the image to be detected. The array or matrix can besubstantially parallel to and at equal distance to the x-ray source. Ina still further example, the detector can be a matrix of detectorsstationarily positioned above the plane of the target structure. In thisembodiment, the deflection surface of the target is appropriatelypitched to generate an x-ray beam that propagates non-planar to thetarget structure and in a direction that intersects with the matrix ofdetectors. Further, the array or matrix of x-ray detectors or x-raysensitive films can detect an x-ray and produce an x-ray image by theinteraction of the x-ray with an individual, group, or portions of theindividual or group of x-ray detectors or x-ray sensitive films.

In embodiments in which the detector is stationarily mounted, thedetector can detect or capture an x-ray image or signal from an emittedx-ray and transfer the image or signal to a computer storage device.Subsequently, the detector is refreshed, thereby prepared todetect/capture the next image. In one example, a suitable detector usedin the step of detecting is a charge-coupled device (CCD).

Referring to FIG. 4, a plurality of x-ray transparent windows 422 can bedisposed in the inner wall 418 of the chamber 410. The windows 422 canbe made of suitable materials, as is known in the art. Additionally, thewindows 422 can be operatively positioned with respect to the imagingzone 416 corresponding to the path of the x-rays 412 to allow thepassage of at least one x-ray beam generated by the plurality ofelectrons from a corresponding one of the plurality of cathodes.Further, the windows 422 can provide a collimating feature to theapparatus. The collimating feature arises from the positioning of thewindow 422 with respect to the propagating path of the generated x-ray.

Field emissive electron sources field emit electrons by applying a biasto a field emissive material and can be individually addressed to emitelectrons varying temporally and spatially. The field emissive electronsources or portions thereof can be addressed by a control voltageindividually, or in predetermined sequences or groupings, to providecontrol over the emitted electron beam and so as to direct the beam toimpact at any one position on the anode target. By this method, multiplepoints of incidence on a target may be impacted in the same device. Ifthe target is made from several different materials, a broader spectrumof emitted x-rays can be generated without having to add and removetargets of different materials from the chamber. Additionally, the useof an array of field emissive sources can be used to reduce the time anyone area of the target is bombarded, thus contributing to reducedheating of the anode.

For example, in an embodiment in which the cathode structure iscircular, the field emissive material can be pulsed in a stepped fashionin which, in every revolution around the cathode structure, the angulardistance between field emissive material addressed by successive pulsesvaries either in a predetermined manner or randomly.

In an additional example, where the field emissive material ispositioned on the cathode structure at a desired interval, the fieldemissive material can be pulsed in successive or non-successive fashionto produce field emission electrons that produce x-rays from the targetcorresponding in angular position and in pulse frequency to theelectrons emitted from the field emissive material. Additionally, thefield emissive material can be pulsed individually or in groups,sequentially or randomly, in a clockwise or counter clockwise rotation,or can be pulsed at a predetermined angular separation. Desiredintervals can include angular separations from approximately 10° to 120°and can include 10°, 15°, 30°, 45°, 60°, 90°, or 120° or variationsthereof.

Further, the cathode can have a rasterization capability. Through theuse of individual, group, or matrix addressing of selected regions ofthe cathode, a rasterized emitted electron beam can be generated anddirected to impinge distinctly at a point of incidence on the target. Bythis arrangement, the stationary cathode can be electrically switched ata predetermined frequency to generate emitted electrons and acceleratethem toward a corresponding incident point on a stationary target.

The emitted x-rays from the stationary target accordingly correspond inposition and frequency to the electrically switched cathodes andgenerate emitted x-rays that can be sufficiently discriminated about theobject to be imaged so as to produce a three dimensional image. Theemitted x-rays are discriminated both in angular position about theobject to be imaged and/or by elevation angle with respect to the objectto be imaged. Further, the predetermined frequency is sufficiently rapidto dynamically image physiological functions of the object to be imaged.In one example, the power can be applied to all of the plurality ofcathodes simultaneously. In another example, power can be applied to asubset (e.g., less than all) of the cathodes sequentially at a frequencyand thereby to electrically switch on and off the generation of x-rays.The frequency can be either pre-set or variably-set (e.g., changed inresponse to a feedback mechanism, either automatically or manually). Inone aspect, the frequency can be sufficiently rapid to image the beatingof a human heart in a CT application. In an exemplary embodiment, thepredetermined frequency in the range of 0.1 Hz to 100 kHz.

FIG. 7 shows a top view of an apparatus for generating x-rays 700depicting a target structure 702 in a substantially circular form. Adetector 704 can be positioned within the hollow 706 of the apparatus700 and can be adapted to allow positioning of an object 708 within theimaging zone. The detector 704 can be operatively positioned to receiveemitted x-rays 710 from the target structure 702 after they have passedthrough the imaging zone. In the FIG. 7 embodiment, two discretepositions are shown generating x-rays. Although two positions are shown,it is to be understood by one skilled in the art that any number ofspatially arranged x-ray generating positions can be utilized. Further,when the cathode is electrically switched, the detector system can bemoved or appropriately activated in a corresponding frequency to thefrequency of switching the power so as to position or activate thedetector to capture the x-ray image.

Additionally, any form of x-ray beam can be generated by the apparatus.For example, an area array of targets can each generate a pencil-likex-ray beam which may correspond to one or more pixels in the detector,preferably no more than ten pixels. Alternately, a line array of targetmaterial can each generate a fanlike x-ray beam which corresponds to oneor more lines of pixels in the detector, preferably no more than tenlines of pixels. Finally, an area array of targets can each generate afan-like x-ray beam which corresponds to an area of no more than 128×128square pixels, preferably no more than 64×64 square pixels. FIG. 8depicts an embodiment of an apparatus 800 in which the target material802 generates a fan-like x-ray beam 804 when bombarded by electrons 806.In FIG. 8, the fan-like x-ray beams 804 image the object 808 intransmission mode and impact a large area array detector 810.Accordingly, the detector 810 is individually addressable (e.g.,pixilated).

The object positioner adjusts the position of an object to be imagedwithin the imaging zone. For example, the object positioner can place anobject between the x-ray source and the array or matrix of the detector.In one example, the object to be imaged is stationarily mounted onto theobject positioner such that a centroid of the object to be imaged ispositioned centrally within the imaging zone. In a CT application, theobject can be a patient suitably oriented within the imaging zone.Further, the centroid can correspond to the physiological function to bemonitored, such as the heart.

A detector is operatively positioned to detect the x-ray after it haspassed through the imaging zone. In one embodiment, the detector can beat a elevation angle to the plane defined by the target structure. Theangle β and corresponding angle γ can be chosen to cause the emittedx-rays to propagate at an angle out of plane to that of the targetstructure, such that the propagating x-rays can be detected by adetector positioned so as not to obstruct the field of view of thetarget, e.g., located above the target structure and across the imagingzone from the origin of the x-rays to be detected. By such anarrangement, the stationarily positioned detector array or matrix doesnot block the x-ray from the target structure (e.g., obstruct the targetwith the backside of the detector) and allows simultaneous imaging ofthe object from all directions (e.g., 360° imaging).

An exemplary method to obtain an x-ray image performed consistent withthe present invention stationarily positions an object to be imaged onan object positioner and positions the object to be imaged within animaging zone, electrically switches a plurality of stationary andindividually addressable field emissive electron sources at apredetermined frequency, each field emissive electron sourceelectrically switched in a programmable sequence to field emit electronstoward an incidence point on a stationary target. The beam of fieldemitted electrons which impact the target generate x-rays by means wellknown in physics. The generated x-rays then exit the chamber through thecollimating windows and image the object to be imaged within the imagingzone. The emitted x-rays are then detected by a suitable detector. Theemitted x-rays correspond in position and frequency to the electricaladdressing of the field emissive electron sources. Additionally, thecircumferential position and/or the elevation angle of the emittedx-rays is sufficiently discriminated with respect to the object to beimaged to produce a three dimensional image.

In an additional method to obtain an x-ray image performed consistentwith the present invention, an object is placed in a device to recordx-ray images, such as the device to record x-ray images as substantiallydescribed herein, power is applied to at least one of the plurality ofcathodes of the x-ray source to generate x-ray radiation for a pre-setexposure time, the object is exposed to the x-ray radiation, and anx-ray image corresponding to the object is captured by either the x-raydetectors or the x-ray sensitive films of the device to record x-rayimages.

In one aspect of the method, the power is applied to all of theplurality of cathodes simultaneously or to a a subset of the pluralityof cathodes sequentially at a frequency. When applying powersequentially at a frequency, the x-ray detectors or the x-ray sensitivefilms can be moved and/or activated at a corresponding frequency to thepower application frequency so as to capture the x-rays produced. Thefrequency can be in the range or 0.1 Hz to 100 kHz. Further, thefrequency can be sufficiently rapid to dynamically image a physiologicalfunction, such as a beating heart.

In a still further aspect, the method provides an imaging environment inwhich the emitted x-rays are sufficiently discriminated with respect tothe object to be imaged to produce a three dimensional image. This canbe a result of the circumferential position and/or the elevation angleof incidence point with respect to the object to be imaged.

Variations of the above described method, as well as additional methods,are evident in light of the above described devices of the presentinvention.

While the present invention has been described by reference to theabove-mentioned embodiments, certain modifications and variations willbe evident to those of ordinary skill in the art. Therefore, the presentinvention is to limited only by the scope and spirit of the appendedclaims.

1-59. (canceled)
 60. An X-ray source comprising: a cold cathode, thecold cathode having a curved emission surface capable of emittingelectrons; and an anode, the anode being spaced apart from the cathode,the anode being capable of emitting X-rays in response to beingbombarded with electrons emitted from the curved emission surface;wherein the cold cathode comprises a plurality of emitters disposed on asubstrate and a gate conductor disposed adjacent the plurality ofemitters, and wherein the plurality of emitters are operative to emitelectrons when a bias voltage is applied to the gate conductor; whereinthe electrons bombard the anode at a focal spot of the anode, whereinthe plurality of emitters comprises a first set of emitters, the firstset of emitters being operative to emit a first electron beam having afirst focal spot with a first shape, and a second set of emitters, thesecond set of emitters being operative to emit a second electron beamhaving a second focal spot with a second shape, the second shape beingdifferent than the first shape, and wherein the first set of emittersand the second set of emitters are located on the same curved emissionsurface and are separately energizable.
 61. An X-ray source according toclaim 60, wherein the electrons bombard the anode at a focal spot of theanode, and wherein a size and shape of the focal spot is determined atleast in part by a curvature of the curved emission surface.
 62. AnX-ray source according to claim 60, wherein the electrons bombard theanode at a focal spot of the anode, and wherein the plurality ofemitters are addressable thereby permitting the size and shape of thefocal spot to be controlled.
 63. An X-ray source according to claim 60,wherein the electrons bombard the anode at a focal spot of the anode,the focal spot being characterized by an intensity distribution whichdescribes intensity of electron bombardment as a function of position,and wherein the plurality of emitters are addressable thereby permittingthe intensity distribution of the focal spot to be controlled.
 64. AnX-ray source according to claim 60, further comprising a vacuum housingand an X-ray transmissive window, wherein the cathode and the anode aredisposed within the housing, and wherein the X-rays exit the X-raysource by way of the transmissive window.
 65. An X-ray source accordingto claim 60, wherein the curved emission surface is fabricated so as tobe curved along a first axis and straight along a second axis which isorthogonal to the first axis.
 66. An imaging system for imaging anobject of interest, the imaging system comprising: (A) an X-ray source,the X-ray source including (1) a cold cathode disposed within a housing,the cold cathode having a curved emission surface, the cold cathodecomprising a plurality of emitters disposed on a substrate, and (2) ananode, the anode being disposed within the housing and spaced apart fromthe cathode, the anode emitting X-rays in response to being bombardedwith electrons emitted from the curved emission surface wherein theelectrons bombard the anode at a focal spot of the anode; (B) a detectorarray, the detector array comprising a plurality of detector elements,the plurality of detector elements receiving the X-rays after the X-rayspass through the object of interest and generating signals in responsethereto; (C) an image reconstructor, the image reconstructor beingcoupled to receive the signals from the detector elements, and the imagereconstructor constructing an image of the object of interest based onthe signals from the detector elements; (D) a display, the display beingcoupled to the image reconstructor, and the display displaying the imageof the object of interest; and (E) an X-ray controller, the X-raycontroller being coupled to the cold cathode to provide control signalsto control the emission of electrons from the plurality of emitters, theX-ray controller being coupled to receive feedback informationpertaining to the operation of the imaging system, and wherein the X-raycontroller adjusts the control signals for the plurality of emitters asa function of the feedback information.
 67. An imaging system accordingto claim 66, wherein the plurality of emitters are addressable, suchthat the X-ray controller provides different control signals thatcontrol different ones of the plurality of emitters.
 68. An imagingsystem according to claim 67, wherein the X-ray controller adjusts thecontrol signals to control a size and shape of the focal spot.
 69. Animaging system according to claim 67, wherein the electrons bombard theanode at a focal spot of the anode, wherein the X-ray controller adjuststhe control signals to control a current density distribution of anelectron beam formed by the electrons bombarding the focal spot.
 70. Animaging system according to claim 66, wherein the cold cathode furthercomprises an insulative layer, the insulative layer being disposed onthe substrate and being located between the plurality of emitters; agate conductor, the gate conductor being disposed on the insulativelayer; and wherein the plurality of emitters are operative to emitelectrons when a bias voltage is applied to the gate conductor.
 71. Animaging system according to claim 66, wherein the imaging system is acomputed tomography imaging system, wherein the system further comprisesa plurality of additional X-ray sources, the plurality of additionalX-ray sources each comprising a respective additional cold cathode and arespective additional anode, wherein the X-ray source and the pluralityof additional X-ray sources are disposed in a ring so as to permit theobject of interest to be imaged without gantry rotation.
 72. An imagingsystem according to claim 71, wherein the system further comprises anX-ray controller, and wherein the X-ray controller sequentiallyactivates the X-ray source and the plurality of additional X-ray sourcesin a manner that simulates rotation of a single X-ray source about theobject of interest.
 73. An imaging system according to claim 66, whereinthe imaging system is a medical imaging system.
 74. An imaging systemaccording to claim 66, wherein the imaging system is a securitycheckpoint imaging system.
 75. An imaging system for imaging an objectof interest, the imaging system comprising: (A) an X-ray source, theX-ray source including (1) a cold cathode disposed within a housing, thecold cathode having a curved emission surface, the cold cathodecomprising a plurality of emitters disposed on a substrate, and (2) ananode, the anode being disposed within the housing and spaced apart fromthe cathode, the anode emitting X-rays in response to being bombardedwith electrons emitted from the curved emission surface; (B) a detectorarray, the detector array comprising a plurality of detector elements,the plurality of detector elements receiving the X-rays after the X-rayspass through the object of interest and generating signals in responsethereto; (C) an image reconstructor, the image reconstructor beingcoupled to receive the signals from the detector elements and the imagereconstructor constructing an image of the object of interest based onthe signals from the detector elements; and (D) a display, the displaybeing coupled to the image reconstructor, and the display displaying theimage of the object of interest (E) an X-ray controller, the X-raycontroller being coupled to the cold cathode to provide control signalsto control the emission of electrons from the plurality of emitters,wherein the electrons bombard the anode at a focal spot of the anode andwherein the X-ray controller adjusts the control signals for theplurality of emitters to control a size and shape of the focal spot. 76.An imaging system according to claim 75, wherein the X-ray controllerpulses the control signals for the plurality of emitters so as to causethe X-rays emitter from the anode to form an X-ray beam that pulsates.77. An imaging system according to claim 75, wherein the cold cathodefurther comprises an insulative layer, the insulative layer beingdisposed on the substrate and being located between the plurality ofemitters; a gate conductor, the gate conductor being disposed on theinsulative layer; and wherein the plurality of emitters are operative toemit electrons when a bias voltage is applied to the gate conductor. 78.An imaging system according to claim 75, wherein the imaging system is acomputed tomography imaging system, wherein the system further comprisesa plurality of additional X-ray sources, the plurality of additionalX-ray sources each comprising a respective additional cold cathode and arespective additional anode, wherein the X-ray source and the pluralityof additional X-ray sources are disposed in a ring so as to permit theobject of interest to be imaged without gantry rotation.
 79. An imagingsystem according to claim 75, wherein the imaging system is a medicalimaging system.
 80. A medical imaging method comprising: generating anX-ray beam at an X-ray source comprising a cathode having a curvedemission surface, the cathode comprising a plurality of emitter conesand a thin film gate, the electron beam being emitted towards an anodeso as to cause the anode to be bombarded with electrons, wherein theX-ray beam is produced in response to being bombarded by the electrons,wherein the electrons bombard the anode at a focal spot of the anode,wherein a size and shape of the focal spot is defined at least in partby a curvature of the curved emission surface, the generating stepincluding emitting an electron beam from the cathode, wherein the X-raysource directs the X-ray beam through a patient, and wherein theemitting step further includes applying a first electric field betweenthe thin film gate and the plurality of emitter cones, the firstelectric field causing the electrons to be emitted from the plurality ofemitter cones, and applying a second electric field between the anodeand the cathode, the second electric field causing the electrons toaccelerate towards the anode; detecting the X-ray beam after the X-raybeam passes through at least a portion of the patient; constructing animage of a portion of the patient based on data collected during thedetecting step; and displaying the image of the portion of the patient.